Qantas had its very own dramatic 'snakes on a plane' episode on Thursday when a three metre python joined passengers onboard an early morning flight bound for Papua New Guinea.

But unlike Samuel L. Jackson's 2006 fictional Hollywood blockbuster in which a nest of vipers cause death and destruction onboard a jet, this reptile was only concerned with its own self preservation.

QF191 was approximately 20 minutes into its 6.15am flight from Cairns to Port Moresby when a woman suddenly pointed outside of the plane and declared to cabin crew: "My goodness there's a snake on the wing... there's its head and if you look closely you can see a fraction of its body too."

While numerous surrounding passengers on board the DHC-8 400 Series scoffed in disbelief, she was in fact correct.

According to University of Sydney snake expert, Professor Rick Shine, the specimen was no other than a "very uncomfortable" scrub python - the longest snake species in Australia."

"There's no way it could be anything else," he said. "They're common in North Queensland. They're ambush predators and if there are rodents anywhere nearby, they'll most likely be in the vicinity. They often find their way into tight ceiling spaces in houses, although I've never heard of one on a plane until now."

Cairns based website designer Robert Weber was one of numerous passengers who witnessed the commotion: "The people at the front were oblivious to what was going on but the passengers at the back were all totally focused on the snake and how it might have got onto the aircraft.

"There was no panic. At no time did anyone stop to consider that there might be others on board."

Mr Weber, 35, said initially, the snake was tucked away "quite neatly" but then the wind caught the last 30cm section of its tail, "pulling him straight out."

He said that from that moment forward, everyone watched on as the trip became "a life and death struggle for the snake".

"I felt quite sad for it really. For the remainder of the flight, he was trying to pull himself back into the plane - even though he was fighting against 400kmh winds. The cabin crew told us that at cruising altitude, it was minus 12 degrees outside there - but not even that was able to finish him."

Mr Weber, who videoed the struggle, confirmed both pilots took it in turns to visit the rear of the plane and watch on with passengers as, several times, the snake somehow hauled itself back to safety, only to get dragged out again. As the snake slowly lost further grip, the wind repeatedly whipped it against the side of the plane, spraying blood across the engine.

"At that point, the pilot turned to us and said: "he should be dead"....yet even on descent, the snake was still fighting to get himself out of the situation he was in."Up until we've landed, I looked out the window and the thing was still moving."

The president of the Australian Licensed Aircraft Engineers Association, Paul Cousins, said: "It appears as though the snake has initially crawled up inside the landing bay, maybe housed himself in there, and then crawled into the trailing ledge flap assembly.

He added: "Nice and warm there but the plane later takes off, the flaps move back and he's probably become shaken because of all the noise and vibration. Once he's moved, he's got caught in the wind."

Mr Cousins confirmed there would have been no way into the cabin for the snake from its original location.

A Qantas spokesperson said: "We have never heard of this happening before.''